If you're okay with quantity over quality, then we will just have to agree to disagree. I would much rather have half of the car list we have now, if everything was really good looking.
I know this is kind of tangential, but more connected than you might think, so I'm going to churn the butter a bit.
This is one of those things that will never be settled between the great divide of Premium and Standard lovers. Some people still won't touch them even with interior view, and the rest will never give them up. By my tag line in my banner, you might guess that I'm a Standard lover, especially when I mention that I have several hundred of them. And race them a lot more than my Premiums.
And this is the thing: racing a car is sure a lot more fun than not racing a car. If you get past the fact that you can't get a clear shot of the Standard's headlight inscriptions in Photo Mode, there are a lot - a LOT - of really nice rides in the Standard list. And most Standards do look quite nice running in the GT5 engine.
But say you're one of those "my way or the highway" types, and it was possible to up the GT5 car list with 300 more Premium models only. Which cars? Only the super, racing and muscle machines? Try and maintain the flavor of Gran Turismo and include a hundred lesser rides? You can count on nothing but fist fights over it, no one will agree on the list and no one will be truly happy with it. If you're going to be stuck with grumblers anyway, I say stick with what we have now and let them grumble over "lesser" vehicles, because more cars are always better than less cars.
As for DLC, no, I don't expect truckloads of Premium cars to bolster the car list on a Forza-like scale. I anticipate in packs of 5 or 10, mostly Standard upgrades. I expect more attention on tracks, mostly classic tracks given to us 2 to 5 at a time. I expect that the Race Mod car list to grow quite a bit, and either livery templates to be included, or some kind of Livery Editor itself. Along with that, a few more bodykit options, mostly of serious brand name items useful for creating race cars, not "rice." I'm looking forward to these new tracks to be incorporated in A-Spec offline as well as online user races and Seasonal Events. I also expect something of our proposed Event Maker to appear at some point, so we can make our own races and championships, on- or offline. I think any three or so from this list will be more than enough to keep the GT5 community involved and invigorated, no matter what competitors do.
On GT6, I expect all cars to be Premium, and most tracks, though a number of them can be "high Standard" in quality and still shine plenty bright. Close-ups of car headlights is one thing, but far fewer people take close-ups of jewelry shop windows, so lesser detail in race locations is much more forgivable. Especially if they feature time of day transition and weather.
On the other hand, the mix of Prems and Std cars worked okay for GT5, but this trick will most likely only fly once. I believe Kaz knows full well that if there's a sniff of dual levels of cars in GT6, the media and fans are going to stage a worldwide riot on his virtual doorstep. If there are two levels, they had better be darn near indistinguishable. I don't foresee any problems in this regard, unless you want 1000-plus cars again. I expect with four years of development on GT6 for there to be not much more than 600 cars, though with a shift of focus on making race courses, a good list of tracks to be there, adding to the 20-something Premium tracks from GT5. Maybe 80 to near 100, and along with that, a terrific load of features and gameplay elements to make everyone happy. And again, on PS4 as a launch or near launch title with a spiffy new wheel to go with it.
@LMSCorvette, I'm way more interested in those tracks to be honest.
. That is enough to me to say PD have money. 
